Signaling system



June 13, 1933,. mm 1,914 2 SIGNALING SYSTEM Filed Jan. 3, 1927 Vo/ume leve/of fiignal at the Head Phones lnteqsz'ty of Impressed High Frequency [mpu/ses Inventor: Dewey TS Lmonds.

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Patented June 13, 1933 pullrsn STATES PATENT OFFICE- orscnnnnorany, NEW YORK, ASSIGNOR '10 GENERAL ELECTRIC comrarw, a oom'ona'rxon or NEW YORK sresmmno sYs'r-EM- v Application filed Ianuary a, 1927. Serial in. 158,454.

"My invention relates to signaling systems and-particularly to systems for the reception of high frequency signaling currents, and h'a's'for its purpose to provide a signaling systern such-that the intensity of the received signal will be automatically maintained at or bel'o 'wa predetermined, level.

i It is well -known'that when the receiving circuits of a high frequency signaling system have heen'adjusted to produce great enough amplification for reception of signals from a distant station the signals from a near by station will be received in much greater vol ume than is desired. Likewise, it may result-that-during reception from a single station'the transmission characteristics of the media over'which the signals are being transmitted may vary'causing the intensity of the received signals to fluctuate thereby necessitating frequent readjustment of the receiving circuit to compensate for the variations in the transmission media and to maintain the1 desired volume level of the received signa Means have heretofore been provided for automatically controlling the transmission level in high frequency systems. These means have usually involved relays which operate responsively to the intensity of the received high frequency impulses to control the power circuit to a motor which affects appropriate adj ustinents'in the transmission circuit. Others have involved relays which operate responsively to the intensity of pilot frequencies transmitted over the same transmission media as the signal, while still others have involved relays which operate responsively to changes in current passed through pilot wires which are subjected to the same transmission conditions as the media. over which the desired signal is bein gtransmitted. Still other means have been provided for manually controlling the'transmission level.

All of these systems have inherent disadvantages in that they either require the presence of a skilled operatoror are complicated in their 'circult construction necessitating the use of auxillary carr1er current generators, pilot wires and the like. Furthermore,

the use ofrelays, motors and other instrumentalities having moving parts introduce disturbances and time delay in the operation of the system which in turn result in undesirable elfects upon the receiver.

The purpose of my invention is to provide an apparatus of the type mentioned, whichwill be entirely automatic in its operation; and which will be simple in its circuit construction and entirely electrical in its operation. By the provision of such an apparatus I have found that the disadvantage of pre viousiapparatus referred to above may be largely eliminated. v v

By my invention I vary the degree of amplification of the signaling circuit in direct electrical response to the intensity of the high frequency impulses which are impressed upon the system.

The novel features which I believe to he characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of best be understood by reference to the following description taken in connection withthe accompanying drawing, in which Fig. 1 illustrates diagrammatically one form of my invention; Fig. 2 presents curves illustrating its operation; and in which Fig. 3 illustrates a modification of the circuit shown in Fig 1. With reference to Fig. 1, 1 illustrates a circuit leading to the usual antenna or wire line depending upon the particular application for which the system is employed. and 3 represent the usual radio frequency amplifiers of the receiving circuit, amplifier 2 being supplied with energy from the input transformer 4 and input circuit 5 which is connected to the control electrode 01' grid 6 ofthe amplifier 2. Likewise, energy is supplied from the output circuit 7 of the electron discharge device 2 through the transformer 8, and tuned circuit 9 to the control electrode or grid 10 of the amplifier 3. 11 represents the detector of the usual receiving circuit.

This detector receives its energy from the out-- operation will.

put circuit 12 of the amplifier 3 through the transformer 16 to the audio amplifier 17 where they are amplified and impressed upon the head phones 18. While the amplifiers 2 and 3. and the detector 11 are shown as of the electron discharge type, it will be apparcut that any type of amplifier or detector may be used. Since the circuit connections of the amplifiers and detector, as thus far described are merely those of a common receiving circuit,-only so much detail is given as is neces sary to an understanding of my invention. The cathodes 19, 20, 21 and 22 of the radio amplifiers 2 and 3, detector 11 and audio am plifier 17 are shown connected to a circuit 23 which is energized through resistance 25 from a suitable source ofpotential 26. Suitable high potential is supplied to the output circuit of the detector 11 from the high potential source 27 through a circuit as follows: cathode 21, cathode conductors 23, conductor 24, source of potential 27, resistance 28, conductor 29, primary winding 30 of the transformer 16 to the anode of the detector 11. The source of potential 27 which comprises the usual B battery of a receiving circuit is provided with an adjustable tap 31 from which a suitable potential may be sup-v plied through conductor 32 and conductor 33' to the anode of the amplifier 2 through the primary winding 33 of the transformer 8, to the anode of the amplifier 3 through the primary winding 34 of the transformer 13- and to the anode of the amplifier 17 through the head phones 18. Likewise, a suitable source of potential is impressed upon the control circuits of the amplifiers 2 and 3 with respect to their cathodes 19 and 20 through a circuit as follows: cathode conductors 23, conductor 24, that portion of the source of potential 27 which is between the conductor 24 and the adjustable tap 24, adjustable tap 24', resistance 35, conductor 36, source of potential 37, conductor 38, thence throu h conductor 39, and a portion of the w 'secon ary winding of the transformer 8 to thecontrol electrode 10 of the amplifier 3, and through the conductor 41 and a portion 42 of the secondary winding of the transformer 4 to the control element 6 of the amw plifier 2. It will be seen that the source of potential 37 is in series with that portion of the source of potential 27 which is between the conductor 24 and the adjustable tap 24'. Hence the efiective potential on the control elements 6 and 10 of the amplifiers 2 and 3 with respect to their respective cathodes will be determined by the sum of these two sources of potential and by the potential'on resistance 35. This biasing potential is normally such that these devices operate principally as amplifiers, and with substantially a minimum of detecting efiect.

- As already explained the resistance 28 is connected .in a circuit including the output current which flows in the output circuit of the detector 11 flows through the resistance 28. Since this current varies in response to the intensity of the high frequency impulses which are impressed upon the detector 11, the potential upon the resistance 28 will correspondingly vary. I utilize this potential upon the resistance 28 as a means for controlling the amplification of the radio amplifiers 2 and 3. To this end the amplifier 43 having an anode 44, a cathode 45 and a control electrode or grid 46 is employed. A suitable source of potential is impressed upon the control electrode 46 with respect to the cathode 45 through an input circuit including the cathode 45, cathode conductors 23, con ductor 24, source of potential 27, resistance 28 which constitutes a variable source of otential, conductor 29, adjustable tap 47, t at portion of the resistance 48 which is between the adjustable tap 47 and adjustable tap 49, adjustable tap 49, that portion of the source of potential 50 which is,between the contact 49 and conductor 51, conductor 51 to the control electrode 46. A portion of the source of potential 50 is closed circuited through the adjustable tap 49, resistance 48 and conductor 52. The purpose of this arrangement will be seen later. A suitable potential is impressed upon the anode 44 of the amplifier 43 with respect to the cathode 45 through an output circuit including the cathode 45, cathode conductors 23, conductor 24, that portion of the source of potential 27 which is between the conductor 24 and the adjustable tap 24, adjustable tap 24, resistance 35, conductor 53 to the anode 44.

For the purpose of preventing alternating current from being supplied from the output of detector 11 to the input of the amplifiers 2 and 3 through the volume control circuits the condenser 55 is inserted between the conductor 29 and the cathode conductors 23 and condenser 56 between the conductor 41 and cathode conductor 23.

The operation of the circuit is as follows: During normal operation when the volume of the received signal is at or below a predetermined level, current will be flowing in the anode circuit of the detector 11 and through the resistance 28. The sum of the potentials in the control circuit of the amplifier 43 which includes the source of potential 27, resistance 28, a portion of resistance 48, and that portion of the source of potential 50 which is between the adjustable contact 49 and the conductor 51 will be such that a strong negative potential will be impressed upon the electrode 46: This being the case, no current will flow in the anode circuit of the amplifier 43 and asa result no voltage will appear upon the resistance 35. The sum of the potential 37 and that portion of the source of potential 27 which is between the adjustable contact '65 circuit of the detector 11. Hence the direct 24' and the conductor 24, is such that the amplification of the amplifiers 2 and 3 will be sity is impressed upon the receiving system.

Then the voltage on the resistance 28 will diminish. and the source of potential 27 will become effective upon the electrode 46 cansing it to assume a less negative or even positive potential depending upon the intensity of the received high frequency impulses. Hence, current will flow in the anode circuit of the amplifier 43 and through the resistance causing a voltage to appear upon this resistance having the polarity indicated in the drawing. Sincethisvoltage is in series with the. source of potential 37 in the circuit of the control elements of the amplifiers 2 and 3, the potential upon the control elements will be increased in a negative direc- 7 tion, thereby correspondingly diminishing the amplification of the circuit and thereby diminishing the intensity of the signals at the receiver.

This operation may best be understood by reference to Fig. 2 in which I have plotted the intensity of the high frequency impulses which are impressed upon the receiving circuit as abscissae and the intensity of the sig nal at the head phones for any given percentage modulation-as ordinates- The curve 1 represents the operation of the circuit when the potential upon the electrode 46 of the amplifier 43 is so strongly negative that no current flows through the anode circuit of this amplifier or through the resistance 35. Assume that it be desired to maintain the volume of the received signals at the head phones at a level indicated by the curve 2. The contacts 47 and 49 will be adjusted to impress a negative potential on the control electrode 43 such that no current will flow through the resistance 35 until the high. frequency impulses impressed upon the detector are of such volume as to produce a signal at the head phones corresponding to the level represented by the curve-2 at the given percentage modulation. Then for all high frequency intensities which produce'si-gnals below this level the amplification of the circuit will be at a maximum and reception will take place on the curve 1. If the volume of the high frequency impulses which are impressed upon the detector 11 become so great as'to cause the volume of the received signal at the head phones toexceed the level represented by the curve 2 then the negative potential on the electrode 46 will be so diminished thatcurrent will flow through the anode circuit of the amplifier 43, causing a diminution in the amplificaiton of the amplifiers 2 and 3. Hence, all high frequency impulses which produce signal intensities above the level 2 at the given modulation will be diminished to this level, whereas, intensities below this volnegative potential ume level will be unaffected. If it be desired to increase the volume level of the received signal, then the contacts 47 and 49 maybe so adjusted that a stronger negative potential will be impressed upon the grid 46. With such an "adjustment a greater volume must be impressed upon the resistance 28 before the on the electrode 46 will be sufiieiently diminished to permitthe flow of current through the anode circuit of the amplifier 43. Hence, only intensities above those represented by the curve 3 will be diminished and reception will take place on the curve 3. By adjusting either of the contacts 47 or 49 in the opposite direction reception can be made to take place upon the cirve 4.

lVith the potentiometer contact 47 adjusted to impress any desired bias on the grid of the direct current amplifier, current starts to build up in the anode circit of the amplifier at a correspondin critical value of input radio frequency voltage to the detector. the radio frequency input voltage to the detector increases beyond this critical value the current in the direct current amplifier increases extremely rapidly, and in a substantially linear relation to the radio frequency input voltage. In this way suflicient control of the amplification is had to maintain the volume of signal at the head hones within a satisfactorily small range 0 variations in intensity.

In Fig. 3 of the drawing 1 have shown a modification of my invention in which the amplifier 46 hasbeen omitted. It will. be

seen that in this case conductors 39 and 41 are connected through the source of potential 37 and the resistance 48, which have been connected in parallel relation for purposes of adjustment, adjustable contact 54 and conductor 55 to the point on the resistance 28,

which is connected tothe output circuit of the detector 11. Hence, it will be seen that any fluctuations in the potential of the resistance 28 will be impressed directly upon the control circuits of the amplifiers 2 and 3. An arrangement of this type may be preferable in av circuit where only small adjustments are required as where the changes in the characteristics of the transm ssion media are small, or in a circuit where a number of amplifiers areused, such that the adjustment is effective upon a number of amplifiers. This arrangement effects a substantial economy in the apparatus required.

While I have describedmy invention with particular reference to a common receiving circuit employing a particular type of detector it will be apparent that it is not so limited but rather that it may be employed in almost any type of high frequency receiving system where a contact volume of output is desired. Likewise, in the embodiment shown I have employed a detector as the controlling tube purely from considerations of economy in the apparatus since, obviously, any type of rectifying device may be em loyed as well.

Furthermore, it will be apparent that the control device may be made to operate upon amplifiers subsequent in the circuit to the controlling tube 11 rather than prior to it as in the embodiment shown and that such an arrangement will have certain advantages such as results from the fact that it entirely eliminates regeneration or any tendency to oscillate. This also enables me to make condensers 55 and 56 of very small capacity, thereby eliminating any time delay in the operation of the device which may be produced by the char ing of these condensers. However, I have ound that with this arrangement greater difficulty is encountered in obtaining substantially horizontal characteristics as shown in Fig. 2 over a large range of inv tensities of impressed high frequency impulses,than is the case in the embodiment shown.

It may thus be seen that I have provided a volume control device which is simple in its circuit structure and its operation and which does not require the attention of a skilled operator, which operates directly in response to the high frequency impulses which are impressed upon the circuit rather than in response to changes in a pilot frequency which is transmitted over the same media as the received signal, or in response to current flowing in pilot wires, which are subjected to the same conditions as the media over which the received signal is transmitted, as has been amount of apparatus and that it may .be applied with facility and without great expense to any of the usual signaling circuits.

While I have shown and described a specific embodiment of my invention, it will be apparent that itis not lim ted to the particular embodiment shown but that many modifications in the circuit arrangements and instrumentalities employed \in carrying out my invention may be made without departing from the scope thereof as set forth in the appended claims.

What T claim as new and desire, to-secure by Letters Patgit of the Unted States is 1. The combmation in a receiving circuit employing an electron discharge amplifier having a control element, a detector and connections whereby current having amplitude dependent upon the characteristics of the transmission medium are supplied to said amplifier and detector, a resistance connected that substantially no current normally flows in the output circuit of said detector, an elec tron discharge device having an anode, a cathode and a grid, said resistance being connected between said cathode and said grid, a second resistance connected between the anode and cathode whereby the potential on said second resistance is dependent upon the output current of said detector and means for varying the potential on said control element in response to the potential on said second resistance thereby to control the amplification of said amplifier.

2. The combination, in a receiving circuit embodying an electron discharge amplifier having a control element, connections where by current having amplitude dependent upon the characteristics of the transmission medium over which currents are received are supplied to said amplifier, means ,for rectifying a portion of said current thereby to produce a source of direct current potential which is variable in response to the intensity of the received current, means for amplifying said direct current potential and for supplying the amplified potential to the control element of said amplifier thereby to control the amplification in response to the intensity of the received current.

3. The combination in a signaling system, employing an electron discharge device hav- 95 ing a grid, means for impressing a biasing potential on said grid such that said device operates principally as an amplifier and with a minimum of detecting effect, means for supplying current to be amplifie to said grid, a. second electron discharge de ice having an anode circuit, a cathode and .a grid, means for impressing a uni-directional biasing potentialon the grid of said second device such in the anode circuit thereof, means for varying said uni-directional biasing potential on the grid of said second device in response to the intensity of the received current and to cause current to flow in the anode circuit thereof when the intensity of received current exceeds a predetermined value and means for controlling the potential on the grid of said first device in response to the current in this anode circuit of said second device th'ereby to regulate the simplification of said first device. l

4. In a high frequency receiving system, sound reproducing means, an electron discharge device having a grid, means for impressing high frequency potential on said grid, means for impressing a biasing potential on said grid such that said device operates principally as an amplifier of said high frequency current andwith a minimum of detecting effect, additional means comprising an electron discharge detector for deriving audio frequency current from the amplified high frequency current and for supplying said current from said detector to the sound reproducing means, and means including said detector for varying the direct current potential upon the grid of said first mentioned electron discharge device only when the high frequency input to said detector exceeds a predetermined value and then to vary said direct current potential substantiallyl linearly with respect to variation in said igh frequency input to said detector thereby to control the amplification of said electron discharge device.

5. In the operation of a carrier wave receiver of the type including a carrier wave amplifier, a detector and an audio frequency output circuit fed from said detector, the method of automatically reducing the effects of varying signal strength which comprises amplifying the direct current potential developed in the plate circuit of the detector, and impressing the amplified direct current potential upon said carrier wave amplifier to control the amplification thereof.

6. In a carrier wave receiver, the combination with a carrier wave amplifier, a detector and an audio frequency output circuitfed from said detector, of an impedance in the plate circuit of said detector, a direct current amplifier connected across said impedance, and circuit connections for impressing the amplified output of said direct current amplifier upon the carrier wave amplifier to control the amplification thereof.

7 A carrier wave amplifier of the vacuum tube type and including circuit elements for 11. The combination with an audion, of means for biasing said audion by a directcurrent voltage, means for automatically varying said bias voltage in accordance with the strength of an incoming signal, at least one of said means comprising a rectifying system including an element having. a critical working voltage, and means where y said critical voltage may be adjusted.

12. In combination, an audion, an out ut circuit therefor, means for suppressing flYlC- tuations in said output circuit due to variations in the strength of an incoming signal, said means comprising a rectifying system having a certain input voltage below which substantially no direct current output is obtained and above which said direct current output rapidly rises and attains an approximately linear relation with respect to the intensity of the signal applied to the input of said detector, and means for adjusting said certain input voltage.

In witness whereof, I have hereto set my hand this 31st day of December, 1926.

. DEWEY T. 'SIMONDS.

automatically impressing upon said amplifier an amplification-control voltage proportional to received signal strength, characterized by the fact that said circuit elements include a direct current amplifier.

8. In combination, an audion, an out ut circuit therefor, means for suppressing uctuations in said out ut circiut due to variations in the strengt of an incoming signal, said means comprising a rectifying system having a critical input voltage below which substantially no direct-current out ut is obtained, and means for adjusting said critical vo ta e.

9. 11 an electrical system, the combination with an audion .having input and output circ-uits, of means for suppressing fluctuations in said out at circuit due to variations in the strength 0 an incoming signal in said input circuit, said means comprising a rectifying system of the type having an approximately linear relation between direct-current output and radio frequency input above a critical input voltage, and means for varying the critical voltage of said rectifying system.

v10. In an electrical system, the combination with an audion, of means energized by said audion for impressing a variable bias on said audion, said means having'a critical working voltage, and means for adjusting said critical voltage. v 

